Federation where resolver is in the extended subgraph/app

[tmCision]

Sorry for the confusing title but I didn't know how to describe what I am looking for.
In all of the examples/documentation that I have read it seems that a type is extended with additional information in the service that provides that information. For example, in dgs-federation-example the Review subgraph extends the Show subgraph and the resolver is in the Review app. What I am trying to figure out is how to do the reverse. Say I had a Location subgraph/app and I wanted to extend the Show subgraph with information on where the show took place. I don't want to have the Location app know anything about shows since its a generic app that can be used by dozens of different apps, but I am not sure how to resolve the location information in the Show app.
Here are the example schemas:
show.graphqls
type Show @key(fields: "id") { id: ID title: String releaseYear: Int locatedIn: Locaion } type Location @key(fields: "id") @extends { id: ID @external }
location.graphqls
type Location @key(fields: "id") { id: ID name: String }